Programming

I am trying to write a program that will;
1) Show the message "Snoozing now...zzzz" on the screen for 5 seconds
2) Then in the same position show the message "The ALARM is going off now!" for 5 seconds
3) Repeat 1) then 2) infinitely until user presses Ctrl C

I can't make it work. Any hints appreciated.
Here is my code;

[me@myplace]$ cat main10.c
/* main10.c
testing signals and alarms */

#include <curses.h>
#include <signal.h>
#include <stdlib.h>
#include <stdio.h>

void handler( void )
{
clear();
mvprintw(10, 10, "The ALARM is going off now!\n" );
refresh();
signal( SIGALRM, handler );
alarm( SIGALRM, 5 );
}

int main( void )
{
clear();
signal( SIGALRM, handler );
alarm( SIGALRM, 5 );
mvprintw( 10, 10, "Snoozing now..zzzzzz\n");
refresh();
endwin();
}
[me@myplace]$ gcc main10.c -lcurses -o mainApp10
main10.c: In function `handler':
main10.c:17: warning: passing arg 2 of `signal' from incompatible pointer type
main10.c: In function `main':
main10.c:24: warning: passing arg 2 of `signal' from incompatible pointer type
[me@myplace]$ mainApp10
Segmentation fault
[me@myplace]$

Where is the curses mode initialized,

Code:

initscr();

Modified your code,

alarm prototype is not correct!

Check this,

Code:

#include <curses.h>
#include <signal.h>
#include <stdlib.h>
#include <stdio.h>

void handler(void);

void handler( void )
{
clear();
mvprintw(10, 10, "The ALARM is going off now!\n" );
refresh();
signal( SIGALRM, handler );
alarm( 5 );
}

int main( void )
{
initscr();
clear();
signal( SIGALRM, handler );
alarm( 5 );
mvprintw( 10, 10, "Snoozing now..zzzzzz\n");
getch();
refresh();
endwin();
return 0;
}

Thanks a lot. matrixmadhan your code almost works perfectly. The only thing it doesn't do is loop infinitely between "The ALARM...." and "Snoozing.....".

It starts by displaying "Snoozing....." than after 5 seconds "The ALARM....". This is good. But then "The ALARM...." stays on screen forever. I want it to then revert back to "Snoozing....." and then back to "The ALARM...." etc etc etc in an infinite loop every 5 seconds.

I will try to modify. Any more hints appreciated.

Although that may be a jolly program, that is far too much code for a signal handler.

C libraries are not "signal safe", the most you should be doing in a signal handler is setting a flag or a minimal bit of IPC to awaken the main program.

If your handler was called in the middle of malloc your heap could get trashed.

One way:

Code:

#include <curses.h>
#include <signal.h>
#include <stdlib.h>
#include <stdio.h>

void handler(int sig) { }

int main( void )
{
        int state;
        signal(SIGALRM, handler);
        initscr();
        clear();
        state=0;
        while(1) {
                if(state) {
                        mvprintw(10, 10, "The ALARM is going off now!\n" );
                } else {
                        mvprintw( 10, 10, "Snoozing now..zzzzzz\n");
                }
                refresh();
                alarm(5);
                pause();
                state=!state;
        }
}

Thanks very much to all. I have a project in mind and this forms a piece of it. I will forge ahead now. You have helped me understand how to implement alarms and signals.